The "Bugs" (or Arachnids, as they are officially known) are an insectoid race of multiple, physically differentiated castes, each with a specialized role in Arachnid society. The Arachnids were originally designed by the Horadrim as a biological weapon in their long and losing war against the Caal. They have an extensive Hivemind collective consciousness which operates instantaneously across even interstellar distances, making it possible for them co coordinate simultaneous activity in multiple star systems. This hivemind is not well understood by human or other alien scientists, and may not have been an intended feature when the Horadrim designed them.
Arachnids come in many shapes and sizes, and there have been multiple reports of new specialized castes being encountered that seemed custom-designed for specific immediate short-term needs, and then never seen or heard from again. However, several castes are common enough that they are considered full-time members of Arachnid society and not one-off breeding experiments or rare mutants.
Worker Bugs: By far the most numerous caste, they dig the subterranean tunnels the Bugs live and fight in, construct and maintain simple machinery, and generally work.
Drones: Barely-intelligent, yet ferocious, low-level melee fighters that are mass-produced and used for swarm-tactic attacks. Basically, they run forward and try to eat you, and their tactics and methods rarely rise above the level of that.
Engineers: A less numerous and more intelligent modification of the Worker Bug, to build and operate more complex machinery and weapons systems.
Soldiers: Smaller and less dangerous in melee combat than Drones, these bugs make up for it with higher intelligence and the ability to use ranged weaponry and more complex tactics of ambush and maneuver.
Warriors: The most dangerous bugs that are frequently seen on the surface rather than in underground tunnel complexes, these larger versions of soldier bugs not only use ranged weaponry and advanced tactics, they also use low- and medium-level magical spells for combat purposes.
Guardians: Oversized and even more dangerous versions of Warrior Bugs that are typically found in chambers deep underground defending Queens.
Kings: The rarest of bugs, these are even larger and more dangerous than Guardians, and are the only bugs that get to mate with Queens and produce offspring.
Queens: The very largest and most dangerous of bugs, these enormous creatures can top 100 meters in length, most of which is a large (and detachable-in-emergency) egg-producing sac extending from the abdomen. They can lay hundreds or even thousands of eggs in a day, and when the eggs hatch a few days to a few months later (depending on caste hatching from them), the newly-hatched bug emerges as a full adult, ready to dig or kill.
Bugs utlilize a form of Organic Technology closely related to that of the Horadrim who created them. Most of their weapons, vehicles, and even starships are either entire living creatures genetically enginee
red and designed to grow into a fully-functional device or part of a larger contraption, or are largely built on structures consisting of the corpses (and occasionally still-living bodies) of a mix of ordinary bugs and specially-grown organisms designed for no other purpose. The bugs wouldn't build a flamethrower out of metal and fuel it with a petroleum-based liquid, but rather would grow a creature that would secrete caustic chemicals which would mix into a hypergolic mixture and ignite, sort of like an oversized Bombardier Beetle, and then carry it into battle and wield it like a rifle. Or they'd simply skip that stage and add that subsystem directly to the DNA of a warrior bug while still in the egg. Even their starfighters are either dead husks of specially-grown organisms piloted by modified warrior "Pilot Bugs" or still-living creatures who have reaction thrusters and weaponry growing out of their bodies. As such, their starships and starfighters are generally inferior in most ways to human designs, but far from helpless in a fight.
Behind the Scenes
The Bugs are one of the reasons the Tech Infantry game exists. The 1997 Starship Troopers film was about to come out, and several college-student fans of the (far, far better) book the movie was based on decided to cross over the setting of the book and the setting of their favorite tabletop role-playing game, "Vampire: The Masquerade" (and its closely-related partner franchises within the World of Darkness series of games by White Wolf Publishing). The idea of werewolves in power armor fighting giant alien insects tickled the part of their brains that never got out of third grade. Additional inspirations for the version of the Bug War trope seen in Tech Infantry come from the novel "Armor" by John Steakley, the "Alien" film franchise, and thousands of pulp science fiction stories and bad B-movies.